Flights were cancelled, homes were flooded, roads became rivers and commuters faced frustrating delays as wild weather lashed Sydney late on Friday afternoon.

The storm front brought damaging winds of up to 100 km/h, large hailstones, heavy rainfall and spectacular lightning strikes across the city.

Domestic and international flights to and from Sydney Airport were affected by the heavy rain and strong winds with a number of planes delayed, diverted or cancelled, leaving a large number of passengers stranded.

Lightning strikes provided a spectacular display ahead of the downpour with many taking to social media to share their photos.

The NSW Rural Fire Service said hundreds of lightning strikes started about 100 new bush and grass fires across the state.

Trains continued to run between Sydney and Gosford, however they were delayed.

The State Emergency Service (SES) responded to 311 calls around Sydney, the Central Coast and Hunter.

In Sydney, most of the storm damage was in Penrith, Canada Bay, in the Wollondilly area near Picton, and in the northern beaches. Wyong on the Central Coast also copped a significant amount of damage.

"We're hearing reports of damage caused by fallen trees and branches, either bringing down power lines or blocking driveways or roads," SES spokesman Phil Campbell said.

"There's around 100 cases of roof damage as well. Some homes have reasonably significant roof damage, but most damage appears to be fairly light."

Three homes at Canada Bay had "some fairly significant roof damage", while an apartment block in Lilyfield had part of its roof ripped off by strong winds. A gust of 95km/h was recorded at Horsley Park in Sydney's west.

The storm followed a hot and humid day for Sydney with the mercury topping 32 degrees in the city and 39 degrees in the west.

The cool change hit the Blue Mountains and Penrith early in the afternoon, bringing relief as well as damaging winds and hail which carpeted Penrith stadium after the temperature dropped from 36.5 degrees at 1pm to 27 degrees just half an hour.

Almost 40,000 homes lost power across the state, spanning from the Illawarra to the Upper Hunter.

Emergency crews worked to restore power outages to 4,200 homes in Sydney's south west, the Penrith district, the Illawarra and Annangrove, Kenthurst and Rouse Hill in the north west.

Sydney residents can expect more rain on Saturday with the Bureau of Meteorology forecasting a high chance of showers in the afternoon and evening and a warm day with a top of 27 degrees in the city.